Electric winches have long been used, especially on utility type, off-road vehicles, for various pulling and lifting tasks. The first shortcoming of prior art has been the personal danger and possibility of winch damage when trying to “park” the winch hook and the inability to “sneak” up on a load. A second shortcoming is the length of time it takes to unwind and rewind the winch rope when there is no load. A third shortcoming is the risk of tangling the winch rope when winching a vehicle that is stuck and suddenly gets traction, causing sudden slack in the winch rope. A fourth shortcoming is the lack of adequate protection features and reliability for the winch motor and/or the electro-mechanical relay control module (i.e. contactor) that powers the winch motor and also reverses the direction of the winch drum. This invention overcomes the first shortcoming by employing a “slow start” mode (or “creep” mode) which automatically switches to a normal winch speed after a short period of time. The second shortcoming is overcome by detecting when the winch is unloaded and after a pre-determined period of time automatically switching to a faster rope speed (boost mode). The third shortcoming is overcome by the fast speed that minimizes the risk of getting a loose rope. The fourth shortcoming is minimized by the many features employed in this invention which include over-current-protection, current-range-adjustment, over-temperature-protection, various protection modes for the external drive, metal oxide semiconductor field effect transistors (MOSFETs), low-battery-protection and reverse-battery-protection.
Prior art to offer multiple winch speeds has been done by changing gear ratios (in the winch gear box) by U.S. Pat. No. 5,927,691 (Otteman), U.S. Pat. No. 4,453,430 (Sell) and U.S. Pat. No. 4,161,126 (Winzeler). Changing gear ratios has a disadvantage because it increases the winch torque by the same ratio as the gear ratio increase, resulting in an increased risk of personal injury and/or winch system damage. One with ordinary skill in the art will readily recognize how gearing affects winch load rating as demonstrated when using a “snatch block” where the winch rope is doubled between the load and the winch. This will cut the retrieval speed in half but also doubles the winch power (e.g. you get approximately 10,000 pounds of pull from a 5,000 pound winch).
Another method to offer multiple winch speeds is by using multiple stator windings with different numbers of poles in an alternating current (AC) motor as used in a shop winch in U.S. Pat. No. 4,145,645 (Price, et al.). This approach is a result of recognizing the benefits of having multiple winch speeds, especially a “creep” mode, but is not automatic and is not practical for a vehicle winch because AC voltage is not typically available. Trolling motors used for fishing have multiple speeds to allow a fisherman to change the speed of the boat. An early method of accomplishing this was to have up to five discrete speeds by using multiple windings and resistors in the winch motor which were selected by switches. More recent trolling motors use pulse-width-modulation (PWM) to power the motor. PWM is the use of a rectangular waveform where battery power is applied to the trolling motor for a period of time and then removed for the balance of the waveform cycle. The duty cycle of this PWM waveform is varied to achieve different motor speeds. Prior art trolling motor speed control is practical but complex, expensive and more difficult to accomplish at the high currents (up to 300 amps and more) required to drive a winch motor.
Yet another prior art that has been used to increase the speed of direct current (DC) motor is to simply apply a higher DC voltage to the motor winding. Such was a common practice in converting antique tractors or other antique vehicles from 6 volt electrical systems to 12 volt electrical systems. The 6 volt starter motor was seldom rewound for 12 volts. It would simply run faster on 12 volts because of the higher torque (since the torque of a DC motor is directly proportional to the motor's armature current), and consequently, make it easier to start the vehicle's engine. This approach is used in the present invention and automatically controlled.
One prior art, U.S. Pat. No. 8,958,956 (Felps) uses electronic control (i.e. solid state) for driving a vehicle winch but has only one winch speed and still uses an electro-mechanical contactor for energizing the winch and reversing the drum direction.